vlookup functions within if functions.

I am making an if function that has 2 vlookups that make up the if false statement. i have it as this =IF(B2>'Item List'!D3,0,=vlookup(A2,'Item List'!A2:F17,4,false)-=vlookup('Item List'!A3,Inventory!A1:E16,2,false)) but i keep getting an error message. I've been working on this for a few hours now and its about to drive me crazy. any help would be a huge help.